The present invention relates to a method and apparatus for synchronously controlling each elevating device of an elevating system having a combination of a plurality of elevating devices.
In the elevating system for elevating an object by synchronously controlling a combination of a plurality of elevating devices such as a jack, an electric motor cylinder, a hydraulic cylinder and the like, in the case in which the amount of elevation of each elevating device is not synchronized, an object to be elevated is tilted dangerously. For this reason, it is necessary to strictly synchronize the amount of elevation of each elevating device.
FIG. 1 is a typical view showing an example of the structure of a conventional elevating system formed by a combination of four elevating devices. In the conventional example, four elevating devices S are coupled through a joint axis R and a gear box G and are driven and elevated by means of an electric motor M to be one actuator. Consequently, mechanical synchronization is carried out. In such a structure in which the mechanical synchronization is carried out, however, it may be impossible to join the elevating devices S through the joint axis R and the gear box G depending on the surrounding circumstances.
It is also possible to apply a structure in which a hydraulic cylinder is used as an elevator and a hydraulic pump is used as an actuator, for example. In that case, it is necessary to connect the hydraulic pump and each hydraulic cylinder through a hydraulic hose. In some cases, however, it is impossible to connect the hydraulic pump and each hydraulic cylinder through the hydraulic hose depending on the surrounding circumstances in the same manner as in the above-mentioned example.
In order to solve the above-mentioned problem, there has been practically used a structure in which electric motors M1 to M4 are respectively fixed to four elevating devices S1 to S4 and are synchronously driven and brakes attached to the electric motors M1 to M4 are synchronously controlled to synchronize the amounts of elevations of the elevating devices S1 to S4 respectively as shown in the typical view of FIG. 2, for example. Each of the electric motors M1 to M4 shown in FIG. 2 should be an induction motor which can be synchronously controlled, for example.
Also in this case, it is possible to adopt a structure in which a hydraulic cylinder is used as an elevator and a hydraulic pump is used as an actuator, for example. In that case, it is necessary to attach the hydraulic pump to each hydraulic cylinder, thereby synchronously driving each hydraulic pump.
In the above-mentioned conventional structure in which an electric motor is attached to each elevating device and is synchronously driven, however, there has been a problem in that synchronization control precision is actually deteriorated. More specifically, on/off control is actually carried out such that a voltage to be applied to each electric motor is binary, for example, 0 V or a declared voltage. As synchronously driving means, a reference one of the elevating devices is determined in advance, the electric motors of other elevating devices are on/off controlled or reversely rotated depending on the operating condition of the reference elevating device, and furthermore, and a speed is regulated by utilizing a brake attached to the electric motor. Consequently, the operations of other elevating devices are synchronized with that of the reference elevating device.
In the above-mentioned method, however, the control is carried out in such a manner that the elevating devices other than the predetermined reference elevating device are synchronized with the reference elevating device. Therefore, also in the case in which the elevating devices other than the reference elevating device are mutually synchronized (within an allowable range), very useless control is carried out so that the synchronization state among the mutual elevating devices is broken away by trying to synchronize all the elevating devices with the reference elevating device.
For this reason, the on/off and reverse rotation control of the electric motor and the use of the brake are carried out more frequently. Consequently, responsibility is deteriorated and synchronization precision is degraded. Since the brake to be used for the electric motor is generally an electromagnetic brake and is originally used for stopping, the responsibility is not very excellent, a lifetime is not very long and noises are made because of frequent use. Therefore, such a brake is not suitable for the use in speed control. Accordingly, there is a new problem in that it is necessary to separately adopt a powder brake or the like having excellent responsibility in addition to the brake for stopping which is originally attached to each electric motor, for example. Such a problem also arises in the case in which a hydraulic cylinder is used for an elevator and a hydraulic pump is used as an actuator, for example.
In order to determine the stop position of the elevating device, conventionally, the control has been carried out in such a manner that a coasting amount is measured in advance after a voltage to be applied to the electric motor is set to 0 V and the voltage to be applied to the electric motor is set to 0 V immediately before the original stop position based on the result of the measurement. However, such a coasting amount is varied according to the load of the elevating device, that is, the weight of an object to be elevated by means of the elevating device. Therefore, there is another problem in that stopping accuracy cannot be maintained. In order to solve such a problem, it is preferable that the coasting amount of the electric motor should be measured in advance according to the weight of the object to be elevated by means of the elevating device. However, this is very complicated practically.
Under such circumstances, the present inventor has proposed the invention filed in Japanese Patent Application No. Hei 10-322626 (1998). The invention filed in the Japanese Patent Application No. Hei 10-322626 (1998) relates to an elevating system control method for synchronously elevating a plurality of elevating devices each of which has an elevator, an actuator elevating the elevator, a driver driving the actuator and a detector detecting a position of the elevator and for moving them to designated movement destination positions by controlling each driver based on a result of detection of each detector for each control period, comprising a first step of calculating a position and a speed of each elevator according to the result of the detection of each detector, a second step of determining a target position where each elevator is to reach before a start point of a next control period based on the position and speed calculated at the first step, a third step of calculating an amount of movement in which each elevator is to be moved before a start point of the next control period based on the target position determined at the second step, and a fourth step of controlling each driver to drive each actuator corresponding to the amount of movement of each elevator determined at the third step, these steps being repeated for each control period.
In the elevating system control method filed in the Japanese Patent Application No. Hei 10-322626 (1998), the amount of movement in which each elevator is to be moved is calculated and the elevator is elevated synchronously for each control period. Therefore, control is carried out with high precision. However, in some cases in which security is maintained depending on the uses of the elevating system, the high precision is not required. In those cases, the invention filed in the Japanese Patent Application No. Hei 10-322626 (1998) is over specialized and a driver such as a servo driver or an inverter is required. Therefore, there is a problem in that the structure of an apparatus is comparatively expensive.